intersubject discrimination: univariate versus multivariate measures

1 intro

Purpose:

To compare univariate and multivariate (multivertex) measures in terms of how well they discriminate subjects.

Description:

• Beta contrast patterns (\(\text{high} - \text{low}\)) were estimated for each run
• with these contrast patterns, two types of euclidean distances were estimated:
  • across-run, within-subject distances
  • across-run, betwen-subject distances
• the mean within-subject distance was subtracted from the mean between-subject distance
• this formed the “multivariate” intersubject discrimintion index (IDI)
• the same procedure was conducted on beta contrast means, to form the “univariate” IDI
• these IDIs were tested against zero, and were also directly contrasted between univariate and multivariate.

Inferential statistics:

• non-parametric bootstrap tests were conducted:
  • subjects resampled, and IDIs recalculated to form bootstrapped distributions
  • 95% intervals were calculated on bootstrapped distributions with BCa method
  • frequentists p-values derived from percentile bootstrap
  • all p-value corrections were performed whole-cortex, with FDR.

Parcellation:

• Schaefer 400, 7 network

GLMs:

• DMCC55B
• run-wise, 1trpk, shifted TENTs
• Cuedts: terms for \(\text{trial-type (congr, incon)}\times\text{sequence (switch, repeat)}\) instead of \(\text{incentive}\)

Target TRs:

• Axcpt: 7, 8, 9
• Cuedts: 9, 10
• Stern: 11, 12
• Stroop: 2, 3, 4

Contrasts:

• Axcpt: \(\text{BY} - \text{BX}\)
• Cuedts: \((\text{InConSwitch} + \text{InConRepeat} - \text{ConSwitch} - \text{ConRepeat})/2\)
• Stern: \(\text{LL5RN} - \text{LL5NN}\)
• Stroop: \((\text{PC50InCon} + \text{biasInCon} - \text{PC50Con} - \text{biasCon})/2\)

Transforms:

• “scaled”: beta coefficients were divided by their root mean sum of squares prior to IDI procedure.
• non-prewhitened patterns

2 stats

3 maps

NB: dark colors are large effects and yellow/light colors are small effectss.

3.1 Axcpt

3.1.1 univariate

3.1.1.1 unscaled

3.1.1.2 scaled

3.1.2 multivariate

3.1.2.1 unscaled

3.1.2.2 scaled

3.1.3 contrast

3.1.3.1 unscaled

3.1.3.2 scaled

3.2 Cuedts

3.2.1 univariate

3.2.1.1 unscaled

3.2.1.2 scaled

3.2.2 multivariate

3.2.2.1 unscaled

3.2.2.2 scaled

3.2.3 contrast

3.2.3.1 unscaled

3.2.3.2 scaled

3.3 Stern

3.3.1 univariate

3.3.1.1 unscaled

3.3.1.2 scaled

3.3.2 multivariate

3.3.2.1 unscaled

3.3.2.2 scaled

3.3.3 contrast

3.3.3.1 unscaled

3.3.3.2 scaled

3.4 Stroop

3.4.1 univariate

3.4.1.1 unscaled

3.4.1.2 scaled

3.4.2 multivariate

3.4.2.1 unscaled

3.4.2.2 scaled

3.4.3 contrast

3.4.3.1 unscaled

3.4.3.2 scaled